<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot></slot>
    </div>
    <div class="dots">
      <span class="dot" v-for="(item, index) in dots" :key="index" :class="{active: currentPageIndex === index}"></span>
    </div>
  </div>
</template>

<script>
  import BScroll from 'better-scroll'
  import {
    addClass
  } from '@/common/js/dom'
  export default {
    name: "Slider",
    props: {
      loop: {
        type: Boolean,
        default: true
      },
      autoplay: {
        type: Boolean,
        default: true
      },
      interval: {
        type: Number,
        default: 3000
      }
    },
    data() {
      return {
        dots: [],
        currentPageIndex: 0,
      };
    },
    mounted() {
      setTimeout(() => {
        this._setSliderWidth()
        this._initDots() //设置轮播的小点
        this._initSlider()
        if (this.autoplay) {
          this._play()
        }
      }, 20)
      window.addEventListener('resize',() => {
          if(!this.slider) {
              return
          }
          this._setSliderWidth(true)
          this.slider.refresh()
      })
    },
    methods: {
      _setSliderWidth(isResize) {
        this.children = this.$refs.sliderGroup.children //轮播图下循环的节点
        let width = 0 //轮播的总长度
        let sliderWidth = this.$refs.slider.clientWidth //父容器的宽度
        for (let i = 0; i < this.children.length; i++) {
          let child = this.children[i]
          addClass(child, 'slider-item')
          child.style.width = sliderWidth + 'px'
          width += sliderWidth
        }
        if (this.loop && !isResize) {
          width += 2 * sliderWidth
        }
        this.$refs.sliderGroup.style.width = width + 'px'
      },
      _initDots() { //初始化轮播小点
        this.dots = new Array(this.children.length)
      },
      _initSlider() {
        this.slider = new BScroll(this.$refs.slider, {
          scrollX: true,
          scrollY: false,
          momentum: false,
          snap: true,
          snapLoop: this.loop,
          snapThreshold: 0.3,
          snapSpeed: 400,
          click: true
        })
        this.slider.on('scrollEnd', () => {
          let pageIndex = this.slider.getCurrentPage().pageX
          if (this.loop) {
            pageIndex -= 1
            this.currentPageIndex = pageIndex
            if(this.autoplay) {
                clearTimeout(this.timer)
                this._play()
            }
          }
        })
      },
      _play() {
        let pageIndex = this.currentPageIndex + 1
        if (this.loop) {
            pageIndex += 1
        }
        this.timer = setTimeout(() => {
          this.slider.goToPage(pageIndex, 0, 400)
        }, this.interval)
      }
    }
  };

</script>

<style lang="scss">
  .slider {
    min-height: 1px;

    .slider-group {
      position: relative;
      overflow: hidden;
      white-space: nowrap;

      a {
        display: block;
        width: 100%;
        overflow: hidden;
        text-decoration: none;
      }

      img {
        display: block;
        width: 100%;
      }

      .slider-item {
        float: left;
        box-sizing: border-box;
        overflow: hidden;
        text-align: center;
      }
    }

    .dots {
      position: absolute;
      right: 0;
      left: 0;
      bottom: 12px;
      text-align: center;
      font-size: 0;

      .dot {
        display: inline-block;
        margin: 0 4px;
        width: 8px;
        height: 8px;
        border-radius: 50%;
        background: rgba(255, 255, 255, 0.5);
      }

      .active {
        width: 20px;
        border-radius: 5px;
        background: rgba(255, 255, 255, 0.8);
      }
    }
  }

</style>
